1. It is possible to produce in the perfused frog's kidney an experimental nephritis which is anatomically similar to that which develops in the living animal.
2. The functional effects of these anatomical alterations may be examined by a method previously described.
3. The correlation of the two aspects of damage, anatomical and functional, is more certain under such conditions than in the living animal.
4. The value of the extravital method in general problems is indicated by our brief consideration of mitochondrial changes.